Cracking of surface materials and other finish systems, such as coatings, applique and/or fastener interfaces, may develop on a variety of structures as the result of environmental stress. Cracks occurring in the finish system may propagate to the underlying structure providing a path for moisture and other environmental species to enter, resulting in corrosion and degradation of the functionality of the finish system and the structures being protected by the finish system.
In many applications, the durability of a material system (e.g., an underlying structure and a finish system) must be tested in order to insure that the finish system can withstand the environment to which it will be subjected. Material system testing may include the process of subjecting the underlying structure and/or any finish systems to thermal cycling (e.g., cycling through two temperature extremes, typically at relatively high rates of change). The material system may be temperature cycled to insure that crack formation does not occur over the desired lifetime of the finish system due to a mismatch in coefficients of thermal expansion of the different material systems or other changes in physical properties.
For example, in the aerospace industry, finish systems (e.g., protective coatings and/or fastener interfaces) for aluminum and/or composite structures must be qualified to determine their efficacy in protecting the underlying structure (e.g., an aircraft) from deleterious environmental exposure in service over the lifetime of the material system and/or the finish system. Thermal cycling testing, designed to simulate the environmental stress experienced over the lifetime of the design, may be both time-consuming and expensive. Thus, it may be problematic to screen a large number of potential material system candidates having different material parameters for the finish system.
Additionally, material system candidates may be tested using environmental chambers that replicate the humidity and temperatures that the underlying structure and the finish system would experience. Operation of environmental chambers to screen for the efficacy of potential finish system may further increase cost and time.
For example, thermal screening of the material system may take months to accomplish before a finish system is fully characterized. This may be due, in part, to the multilayered nature of many finish systems and the large number of parameters that need to be optimized and taken into account. After a material system candidate has been developed, a single thermal cycle (e.g., a cycle sufficient to cause the finish system to expand and contract) may take many hours. Numerous thermal cycles may constitute a testing block (e.g., 1 testing block=400 thermal cycles). Numerous testing blocks may need to be repeated to adequately simulate a typical service life of the material system candidate (e.g., the design of the underlying structure and/or the finish system) and/or before cracks appear.
Therefore, screening of just one potential finish system candidate may be tedious, time consuming and expensive using conventional testing solutions.
Accordingly, those skilled in the art continue with research and development efforts in the field of material testing and, in particular, testing for cracks in surface finish systems.